A general description of weaving and general descriptions of the known air weft projection techniques in the art, including a theoretical analysis of the projection of wefts by means of a moving gaseous stream, which constitute part of the "Background of the Invention and Prior Practice" of this invention appear under the same heading in application Ser. No. 64,180 above, and are incorporated by reference herein in entirety.
Irrespective of the particular category of air weft insertion system, the delivery of the strand to the system plays an important part in the practical success or failure of the system itself and heavy attention has been directed in this art to designing an developing strand handling or delivery systems which would satisfy the rather special requirements which are inherently created by air weft insertion. In general, these efforts have resulted in excessively complicated arrangements which are prone to failure over long periods of time and moreover must be operated in fairly critically controlled timed relation to the weaving cycle of the loom. It would obviously be advantageous in the art to simplify the delivery of the strand to the air weft insertion means.
An even more critical aspect of the strand delivery problem is the maintenance of effective control over the length of the strand as it is being propelled through the shed of the loom under the impetus of the air insertion means. The criticality of this problem distinguishes an air weft insertion system from a liquid, i.e. water, insertion system since in the latter the leading end of the weft length to be inserted is physically adhered to the column of water that is being projected across the shed and moves bodily therewith so that the leading end of the strand and the leading end of the water column must move across the shed as an integral unit and arrive at the opposite side of the shed at the same moment. Thus, in a water injection loom, the projection of the water column and strand is reduced simply to a "ballistics" analysis, e.g., whether the mass of the water being projected and its velocity is adequate to traverse the particular length of the shed and pull the weft length therebehind.
The operative circumstances are entirely different in an air insertion system wherein the "air column" and the leading yarn end cannot arrive simultaneously, especially with the realization that, in fact, the existence of any discrete "air column", in the sense of a coherent column of air which maintains its integrity during its travel from one point to another is almost certainly out of the question, due to the fact that the starting "air column" completely loses its identity during passage through the shed, at least when the insertion system includes the interrupted guidance tube, as is preferred for reasons explained in the incorporated material above.
Thus, the burst or pulse of air that actually arrives at the opposite side of the shed cannot be the same burst or pulse of air that was initially emitted by the insertion means and, indeed, it can be proven mathematically that the burst of air that is perceived at the reception end cannot be the same air emitted from the insertion means. The phenomena occurring within the guidance tube as the air pulse passes therethrough are too complex to permit a full understanding at this time, but it is clear that the behavior of the air pulse is radically different from the behavior of a water stream due to the inherent difference in the nature and behavior of moving streams of air and water.
In general, prior art air weft insertion systems elected to so deliver the air that the critical problem of maintaining control over the delivery of the projected strand is minimized by simply prolonging the burst of air emitted from the insertion means as needed for the strand to move the required distance, or alternatively, further nozzles are inserted within the shed to in effect prolong the air flow. Thus, the prior art insertion means is caused to emit a burst of air for whatever length of time is required to insure that the weft strand is projected entirely across the full length of the shed and the high consumption loss of compressed air accompanying this technique is accepted as an unavoidable necessity. Inherent advantages are possible by the utilization instead of a high energy short duration burst of air, as is the objective of an improved overall weft insertion system in which the present invention is preferably associated and is disclosed in such association herein, but under such circumstances, the problem of strand delivery becomes particularly critical. Such high energy pulses impart such acceleration to the strand that the leading end tends to be overrun by trailing portions as it encounters the frictional resistance of the atmospheric air that it must penetrate, resulting in the creation of undesirable tangles in the inserted weft.